This invention relates to a pressure regulating valve for installation in a vent duct in an internal combustion engine.
Pressure regulating valves of this kind are used, for example, in the vent duct between the crankcase and the intake manifold or air filter. Another typical application is installation in the vent duct of the fuel tank. In either case the object is to prevent the pressure or the partial vacuum in the space being vented from increasing beyond a certain level.
German Utility Model No. DE-G 78 22 216 discloses a pressure regulating valve which contains only a single valve device comprising a diaphragm which controls passage through the mouth of a vent passage and closes the passage if necessary. To enable a sufficient amount of gas to be vented through the pressure regulating valve when a relatively slight vacuum prevails at full load operation corresponding to a wide-open main throttle valve in the engine's intake manifold, the mouth of the vent passage must be rather large. If a greater vacuum occurs in the intake manifold, for example due to the closing of the main throttle valve, this vacuum exerts a considerable force on the diaphragm through the orifice of the vent duct when the pressure regulating valve is closed. It would be possible to counteract this force only with a correspondingly strong valve spring. But the result would be that the diaphragm would have to have an undesirably large diameter in order to be able to perform its regulating function as well at lower vacuums. Consequently, this known pressure regulating valve only functions well if the fluctuations of the vacuum needed for venting remained within relatively narrow limits.
Another pressure regulating valve is disclosed in Bendig, U.S. Pat. No. 4,373,499, which attempts to avoid this disadvantage. This valve operates with two diaphragms connected in parallel. Each diaphragm is spring loaded, and each spring and diaphragm is designed so that the valve that has the larger valve opening closes first when a certain vacuum level is reached, and the second valve, which has a smaller valve opening, also closes if a still higher vacuum occurs. Thus this valve can be used even if the vacuum used for venting fluctuates considerably.